1. Field of the Invention
The present invention relates to a line-of-sight detection technique used for an input device of a computer or for an auxiliary driving device when driving a vehicle.
2. Description of the Related Art
A line-of-sight detection technique has been studied as an input device of a computer for handicapped people who can not freely use their hands or fingers. The line-of-sight detection technique is also used as an auxiliary driving device of vehicles by monitoring the line of sight of a driver who is driving a vehicle. However, some line-of-sight detection apparatuses of the related arts require a user to wear a specific equipment, and since these techniques place restrictions on a movement of a user, their usability is unsatisfactory. In order to solve this problem, a technique of detecting the line of sight by using an eyeball model has been developed.
When an eyeball model is used, it becomes significant that an accurate distance from the position whereat a camera is located to the face of a user is obtained correctly by a simple method. For example, an apparatus disclosed in JP-A-8-297019 (line-of-sight measuring apparatus for vehicles) is an apparatus that detects the line of sight of a driver, and uses a distance sensor as a device that obtains the distance from the position whereat a camera is located to the face of the driver. As a distance sensor, an ultrasonic sensor or the like is used. However, when the ultrasonic sensor is used, the entire apparatus becomes complicated, while the detection accuracy would be reduced when a simpler sensor is used, and the apparatus would become too expensive when high accuracy is provided.
A technique of detecting the line of sight by using an eyeball model is also described in “An eye tracking system based on eyeball model”, Information Processing Research Report 2001-HI-93, pp. 47-54, 2001, and “An eyeball-model-based eye tracking method”, Eighth Image Sensing Symposium, pp. 307-312, 2002. In the apparatus described in these documents, near-infrared ray is irradiated to a cornea in the eye from a point light source, and obtains the distance from a camera (or the point light source) to the face in order to obtain coordinates of a reflected image (called as a Purkinje image). A focus value when a focus is adjusted to a position whereat the size of the point light source (the size of the Purkinje image) is the smallest In an image obtained by the camera is employed to obtain the distance. However, it is difficult to adjust the focus so that the size of the Purkinje image becomes smallest in exactly, and accordingly, an accurate distance measurement can not be expected. Further, there might be some error in the detection of the line of sight using the obtained distance.
Calibration may also be employed as a method of obtaining the distance between a camera and an object in real space. According to this method, however, the measurement system would be complicated as a coordinate model of the three-dimensional coordinate system is required in real space for calibration.